dxtxpx
Forum Guru
Topics: 259
Posts: 1,233
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A retired auto worker was diagnosed with TB. He had been ill for about 9 months with sx which included intermittent fever, night sweats and a productive cough. He noted a marked wt loss of 50 lbs. A sputum smear showed the presence of numerous Gm+ acid fast bacillil. Several of his co-workers were shown to be skin test positive with tuberculin (PPD) test
I) Transmission of causative agent Mycobacterium tuberculosis between humans is primarily thru
a) sexual contact
b) respiratory droplets
c) contaminated foods
d) soil (enviornment)
e) contaminated blood products
II) It would be advisable for the above pt to undergo further testing with
a) another skin test
b) CT scan
c) Chest Xray
d) NMR scan
e) bacterial culture isolation
III) Many virulent strains of bacterium have been shown to contain
a) PPD
b) small RNA plasmid
c) flagella n pili
d) cord factor
e) potent exotoxins
IV) An e.g., of atypical mycobacteria found frequently in conjuction with IC pts such as AIDS would be
a) M kansasii
b) M marinum
c) M smegmatis
d) M scrofulaceum
e) M acium-intracellulare
V) Early stage of M tuberculosis is characterized by formation of which of the following lesions in lungs
a) granulomatous
b) exudate
c) tubercule
d) eschar
e) induration
VI) Which of following drugs is least likely to be effective in tx of TB
a) cholramphenicol
b) isoniazid
c) rifampin
d) ethambutol
e) pyrazinamide
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| drmka
Forum Junior
Topics: 1
Posts: 59
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respiratory droplets...it is called fluddge droplets...
chest x-ray is enough,ct is better to show cavitaries...
chord factor...
M.avium-intracellulare...
eschar
INH
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| auubar
Forum Senior
Topics: 30
Posts: 182
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I think v is granulomatous and vi is chloramphenicol
:?:
auubar
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| alice8
Forum Guru
Topics: 37
Posts: 643
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respiratory droplets...
chest x-ray
chord factor...
M.avium-intracellulare...
eschar
chloramphenicol
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Dream on 'til your dream comes true.
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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respiratory droplets..
CXR...
Cord factor..
MAI.......
tubercle.......
chloramphenicol...
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| dxtxpx
Forum Guru
Topics: 259
Posts: 1,233
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Correct answers:
I) b (resp droplets)
II) c (chest xray)
III) d (cord factor)
IV) e (M avium intracellulare)
V) b (exudative)
VI) a (chroamphenicol)
Mycobacterium tuberculosis, the causative agent of the dis, is acquired by inhalation of resp droplets from infected individuals. Intial infection therefore takes place in the lungs with the formation of exudative lesions which progress into granulomatous and finally tubercle lesions consisting of walled-in bacteia, giant and epithelioid cells surrounded by fibrosis and calcification.
The highly immunogenic nature of mycobacterial cell wall elicits a strong cell-mediated immune response. PPD, administered intradermally, produces induration (thickening) and erythema (redness) in area of injection in previously exposed individuals. Induration of >10mm within 48-72 hrs indicates a positive skin test. Virulence in bacteria is closely correlated with the presence of cord factor (trehalose dimycolate) in the organisms. Most Mycobacteria so display slow growth rates. The cell mediated immune response attempts to restrict the spread in healthy individuals, therefore IC individuals are more prone to infections. M avium intracellulare is an atypical mycobacterium and has been observed with high frequency in such pts. Antibiotic therapy usually consists of combo of INH, rifampin, ethambutol, or pyrazinamide, sometimes for more than 6 months. The extended period is necessary because of slow-growing nature of bacteria and is to enable the drugs to permeate granulomatous and tubercle lesion
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| bactitech
Forum Elite
Topics: 25
Posts: 499
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Acid fast bacilli are never described by a Gram reaction. Acid fast bacilli CAN stain gram positive on a gram stain, but they CANNOT be differentiated as ACID FAST unless an AFB stain is performed. The classic stain is ZN (Ziehl-Nielsen) but most labs use an Auramine fluorescent methodology nowadays for direct smears as it is much easier to spot the little buggers if they fluoresce. ZN is used to confirm once the buggers grow.
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Clinical Microbiology since 1974
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| Malaysian
Forum Guru
Topics: 28
Posts: 778
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bactitech.......I'm sure you have heard of L-J mediums to grow them......can you tell me the function of malachite green in these medium and also whats so special about this medium that its mainly to grow the myco. tuberculosis??
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| bactitech
Forum Elite
Topics: 25
Posts: 499
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I know that LJ is blue/green, but to be honest, I never knew that malachite green was the reason. Therefore, I don't know the function of it.
LJ is an egg-based medium. It will grow most acid fast bacteria, including MTB (there are others). AFB are very fussy and take quite awhile to grow. This is part of the reason it took Robert Koch so long to find the causative agent for TB back in the late 1800's.
Labs are also required nowadays to use a liquid medium for possible earlier detection of AFB. MTB takes about 3 weeks to grow on LJ. We also set up MGIT (TM) tubes with all our AFB cultures. We use a blacklight to see if they fluoresce. If they fluoresce, we stain them and, if they show AFB, subculture them out. I believe they also do probe testing for MTB, but to be quite honest, I haven't done AFB workups in at least ten years so I'm not sure what the sequence of events is if they are positive.
Bacterial contaminants will also cause fluorescence, hence the staining before subculturing. Most of the time, fluorescence is due to bacteria, so the MGIT must be re-digested and re-set up.
http://www.bd.com/Clinical/products/mycob/mgit960...
We do NOT have the big 960 system shown on this web page, as we don't do nearly this large of a volume.
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Clinical Microbiology since 1974
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